Such a method is known from EP-B-0.108.635, according to which an amount of cyclic monomers and an amount of catalyst are transferred to a glass reactor under dry conditions, for example under a dry stream of N.sub.2. The reactor is sealed and the monomers and the catalyst are melted and mixed. The polymer is removed from the reactor on completion of the reaction.
In view of the fact that a polymerized polymer of cyclic esters is a rigid piece of material, it is usually only possible to remove the material from the reactor by breaking the glass wall of the reactor. This is a great drawback for applications on an industrial scale, characterized by the production of many pieces of material.
With a method according to EP-B-0.108.635 the material obtained has to be processed by milling or melting in order to obtain an object with a usable shape. Milling presents the drawback that a large amount of waste is obtained, which is economically and ecologically disadvantageous. Melting presents the drawback that the microscopic, molecular, structure of the material obtained immediately after polymerization, the so-called "as polymerized" material, is lost. Several publications state that the "as polymerized" structure presents advantages; see for example Makromol. Chemie, 188, pp. 1809-1814, 1987.
Moreover, a number of bonds in the polymer will be broken in melting and as a result the molecular weight of the polymer will decrease.
With a reactor without a separate mixing chamber as in the conventional method, in order to mix the monomer and catalyst composition the entire reactor is shaken or a magnetic stirring bar is used. Neither of these methods leads to a desirable degree of mixing of the catalyst and monomer. On the other hand, by mixing the catalyst and monomer in a specially designed mixing chamber, a much better mixing occurs. Furthermore, when a stirring bar is used, there is the undesirable result of having the stirring bar incorporated in the product.